Epithelia create barriers and regulate solute and water transport through transcellular and paracellular pathways. The paracellular pathways of different tissues vary remarkably in size selectivity, ionic charge selectivity and transepithelial electrical resistance (TER). The claudin family of transmembrane proteins is responsible for conferring these variable properties. In order to better understand the contribution of paracellular transport and claudins to the function of an epithelium, the properties conferred by cell-specific expression and localization of individual claudins need to be better understood. Here, we explore the properties of claudin- 14 and the localization pattern of claudins in the liver. Expression of human claudin- 14 significantly increases TER and decreases permeability to sodium. Quantitative PCR revealed hepatic expression of 9 of 16 claudins tested at levels varying as much as 700-fold. Immunofluorescent localization revealed localization of claudins- 1, -2 and -3 to hepatocytes, claudin-5 to endothelial cells, and claudins-3, -7 and -8 to cholangiocytes.